The present invention relates to load power switching circuits and, more particularly, to novel integratable load voltage sampling circuitry for apparatus controlling the R.M.S. magnitude of an A.C. voltage across a load.
It is known to control the magnitude of a current flowing through a load from an A.C. source by means of a phase-control circuit, utilizing either forward-phase control or reverse-phase control (the latter as described and claimed in co-pending application Ser. No. 529,296, filed on Sept. 6, 1983, now U.S. Pat. No. 4,528,494, issued July 9, 1985 assignee of the present application and incorporated herein in its entirety by reference). In many uses, open-loop control of the load voltage magnitude, and therefore of the load power, is adequate. In many other uses, e.g. a line voltage converter for energizing lower voltage incandescent lamps, closed-loop control of the load (lamp) voltage magnitude, and therefore of the load power, is desirable. It is also desirable that any load voltage magnitude control apparatus (controlling the "average", i.e. root-mean-square (R.M.S.), magnitude) be utilizable with any switched-voltage or phase-control (whether forward-control or reverse-control) voltage converter and also be equally as well suited for use with power switching devices, placed in series between the controlled load and an A.C. source, of regenerative or controlled-turn-off types. It is also highly desirable that any load voltage magnitude control apparatus be capable of operating in conjunction with load current control means, such as the reverse-phase load current control means of the aforementioned co-pending application, which provides load control during the high "inrush" current magnitude initial interval when a "cold" load is first energized. One such average load voltage control means is described and claimed in allowed co-pending application Ser. No. 561,494, filed Dec. 14, 1983, by Milton D. Bloomer, assigned to the assignee of the present application and incorporated herein in its entirety by reference. Bloomer's apparatus uses a load voltage sampling means which requires a plurality of fixed-value resistors each of which must be maintained fairly closely in absolute and relative value. His circuit is thus neither easily implementable in completely integrated circuit form nor is such a circuit capable of an implementation at as low a cost as can be desired. A lower-cost, completely-integratable load voltage sampling circuit is therefore highly desirable.